1. Field of the Invention
The present invention relates to a field emission displaying device and its driving method, and more particularly to a field emission displaying device in which a scan pulse is supplied to a scan line and a data pulse is supplied to a data line so as to drive each cell of display device according to a voltage difference between the scan pulse and the data pulse, and its driving method.
2. Description of the Background Art
Recently, various flat display devices that are capable of reducing a weight and volume of a cathode ray tube (CRT) are being developed.
The flat display devices include a liquid crystal display, a field emission display (FED), a plasma display panel and an electro-luminescence, and in order to improve a display quality of those flat display devices, researches and developments are being actively conducted to heighten a luminance, a contrast and a color purity.
Among them, the FED includes a tip type FED that emits electrons by using a tunnel effect by concentrating a high electric field to an acute emitter, and a flat type FED that emits electrons by concentrating a high electric field to a metal having a certain area.
In the tip type FED, a voltage is supplied to a gate electrode to apply an electric field to an electron emitting portion, so that electrons are emitted from a conic protrusion portion made of silicon or molybdenum.
Meanwhile, the flat type FED has a structure that a metal layer, an insulation layer and a semiconductor layer are stacked, and electrons are injected to pass the insulation layer by using the tunnel effect from the metal layer and emitted outwardly from an electron emitting unit.
As for the tip type FED, an electron emission amount is determined according to the characteristics of an emitter used for the electron emission.
Thus, emitters are to be fabricated to be uniform, but with the current fabricating process, it is not easy to fabricate emitters exactly the same with each other and much time is consumed for the process for fabricating the emitters.
In addition, since electrons are emitted from the acute emitter, scores of bolt and hundreds of bolt voltage should be applied to a cathode electrode and a gate electrode, causing a problem of much power consumption.
FIG. 1 is a drawing illustrating a cell of a flat type FED in accordance with a conventional art.
As shown in FIG. 1, each cell of the flat type FED includes an upper substrate 101 on which an anode electrode 102 and a fluorescent material 103 are stacked, and a field emission array 105 formed on a lower substrate.
The field emission array 105 includes a scan electrode 108 formed on the lower substrate, an insulation layer 107 formed on the scan electrode 108 and a data electrode 105 formed on the insulation layer 107.
The scan electrode 108 supplies current to the insulation layer 107. The insulation layer 107 insulates the scan electrode 108 and the data electrode 106. The data electrode 106 is used as a fetch electrode for fetching electrons.
The flat type FED in accordance with the conventional art constructed as described above will now be explained.
In order for a picture to be displayed on the display device, first, a scan pulse of a negative (−) polarity is applied to the scan electrode 108 and a data pulse of positive (+) polarity is applied to the data electrode 106. And an anode voltage of positive polarity (+) is applied to the anode electrode (102).
Then, electrons are accelerated toward the anode electrode 102 after tunneling from the scan electrode 108 to the data electrode 106 and to the insulation layer 107.
The electrons collide with the fluorescent material 103 of red, green and blue color and excite the fluorescent material 103.
At this time, a visible ray of one of red, green and blue color is generated according to the fluorescent material 103.
Since the scan electrode 108 and the data electrode 106 are installed facing each other with a certain area, the flat type FED can be driven at a lower voltage compared to the tip type FED.
In other words, since only a few V to 10 V voltage is applied to the scan electrode 108 and the data electrode 106 of the flat type FED and the scan electrode 108 and the data electrode 106 emitting electrons have a certain area, the scan electrode 108 and the data electrode 106 can be fabricated by a simple process compared to the tip type FED.
FIG. 2 is a drawing illustrating driving waveforms supplied to the FED in accordance with the conventional art.
As shown in FIG. 2, a scan pulse (SP) of negative polarity is sequentially supplied to scan lines (S1, S2, . . . , Sm) of the conventional FED, and a data pulse (DP) of positive polarity synchronized with the scan pulse (SP) of negative polarity is supplied to a data line (D).
Electrons are emitted from the cell where the scan pulse (SP) and the data pulse (DP) have been supplied, by a voltage difference between the scan pulse (SP) and the data pulse (DP).
FIG. 3 is a drawing illustrating a cell arrangement of a general FED.
As shown in FIG. 3, if −5V scan pulse (SP) is applied to a first scan line (SI) and 5 v data pulse (DP) is applied to the data line (D), 10 V of voltage difference occurs at the first cell (P1) formed at the first scan line (S1). Accordingly, electrons are emitted from the first cell (P1) to which the data pulse (DP) has been supplied.
Meanwhile, only 5V of data pulse (DP) is applied to the second through mth cells (P2 through Pm) formed at the mth scan line (S2 through Sm), no electrons are emitted.
Thereafter, the above process is repeatedly performed to sequentially apply the scan pulse (SP) and the data pulse (DP) up to the mth scan line (Sm), so as to drive the first through the mth cells (P1, P2, . . . , Pm) and display a picture on the display device.
After the picture is displayed, a reset pulse (RP) of positive polarity is applied to the first through the mth scan lines (S1, S2, . . . , Sm). Then, electric charges charged in the first through the mth cells (P1 through Pm) are removed.
However, in the conventional flat type FED, when the first scan line is driven, the data pulse is applied also to the second through the mth scan lines. A certain voltage is applied to the second through the mth scan lineswhich have received the data pulse, and a capacitance value of the cells becomes great due to the certain voltage. This phenomenon also occurs when the cells formed at the second through the mth scan lines are driven.
In other words, in the conventional flat type FED, when the scan pulse is applied to one scan line, since the data pulse is applied to every scan line, the cells are not uniform. When the cells are operated in a state that they are not uniform, a picture quality of the FED is degraded.
In addition, the driving speed is degraded due to the value of the capacitance charged in the cells that are not operated, so that the driving efficiency is degraded.
Moreover, the reset pulse (RP) is simultaneously applied as a square wave to the first through the mth scan lines (S1, S2, . . . , Sm). In this respect, since the flat type FED is formed in a capacitor structure including a metal layer, an insulator layer and a metal layer, it has a great capacitor component and a diode quality, a displacement current having a great instantaneous peak value flows in a reset output wave current applied to the cell.
The displacement current causes a breakdown of the insulation layer 108 between the scan electrode 108 and the data electrode 106 only to shorten a durability of the electrode and damage a driving IC for driving the FED.
In addition, a displacement current having a great peak value increases a reactive power that is not contributed to emitting, causing a problem of a power loss.